Romans 15:23 But now having no more place in these parts, and having a great desire these many years to come unto you;
Paul is leaving because there is no more place for him. There is no room for him to do ministry. That didn’t mean that there wasn’t much to be done but it did mean that he had trained men and got the work started. Once there were others that could do the work he left.
He was the foundation builder. He went where others had not yet gone. He got things started then he moved on.
Missionaries could learn a great from this lesson. We start and then we move on to another place.